Predestination Paradox

A predestination paradox, also called either a causal loop, or a causality loop and (less frequently) either a closed loop or closed time loop, is a paradox of time travel. It exists when a time traveler is caught in a loop of events that "predestines" his or her journey back in time. Because of the possibility of influencing the past while time traveling, one way of explaining why history does not change is by saying that whatever has happened must happen. A time traveler attempting to alter the course of history in this model would only be playing their part in shaping history as we already know it, rather than changing any aspects of the past. This is regardless of the time traveler's intentions or efforts to preserve their personal experience, or knowledge, of events.

Xeno Offensive
The predestination paradox was an integral part in the Season 2 crossover episode "Xeno Offensive". There is one main example where a future time traveler goes back in time and fulfills their role in history (rather than changing it): This predestination paradox is heavily tied to the concept of fate. Xeno's own creation is an example of this: Xeno's attack on Earth in the past caused his creator to create Xeno to prevent things like this from happening again. This heavily suggests that the events in "Xeno Offensive" fulfilled the predestination paradox: Xeno unknowingly traveled back in time fulfill his role in history as the greatest threat to the Earth and Zero's archenemy.
 * Xeno's offensive leading to his creation - After fighting Zero in the future, Xeno goes back in time to do his "Xeno Offensive" all over again in the past. This event causes a younger version of Xeno's own creator to create Xeno so that he could protect the Earth from threats.